A conventional variable siphon water closet has been disclosed in Korean Patent No. 479678. As shown in FIG. 1, the water closet includes a flexible water bladder 5 installed at a rear side of a bowl 1 to be connected to a water supply passage 3; an upper bracket 7 for coupling the water bladder 5 with the water supply passage 3; a lower bracket 9 coupled with a bottom surface of the water bladder 5; tension springs 11 for resiliently connecting both ends of the upper and lower brackets 7 and 9, respectively; a variable siphon tube 13 including one opening end 13a connected to a water outlet 1a of the bowl 1 through an upper bellows tube 15, another opening end 13b connected to a bottom tube 19 through a lower bellows tube 17, and a bent portion 13c coupled with the lower bracket 9; and a small tube 21 for connecting the water bladder 5 to the variable siphon tube 13.
However, the aforementioned conventional water closet has the following problems.
1. In the above conventional water closet, the variable siphon tube has a long length (e.g., U shape) and is connected to the bottom tube through the lower bellows tube. Therefore, tension springs with a strong elastic force are essentially required to lift and lower the variable siphon tube. Further, since the tension springs have a strong elastic force, a capacity of the water bladder should be increased such that the springs can be stretched enough to lower the variable siphon tube. Therefore, since a large amount of water discharged from a water tank flows into the large water bladder, an amount of water that should be introduced into the bowl is reduced accordingly, which results in reduction of flushing efficiency of the bowl.
2. In addition, to achieve an aesthetic external appearance, parts installed at the rear side of the bowl are covered with a ceramic material (a class of ceramics). A process of manufacturing a ceramic toilet in this manner has a lower productivity and thus results in increase of the manufacturing costs of products.
3. As shown in FIG. 1, the two springs are installed at both sides, i.e. at two positions, respectively. The elastic forces of the two springs should be the same as each other, if the variable siphon tube can be stably lifted and lowered. If the elastic forces of the two springs are different from each other or there is a difference in installation positions of the springs because the bottom of a water tank of the water closet is not level in a ceramics manufacturing process, the variable siphon tube is unstably lifted and lowered. This causes abnormal wear to the water bladder and the upper and lower bellows tubes installed at both ends of the variable siphon tube
4. Particularly, as shown in FIG. 1, since the springs are installed externally at both sides of the variable siphon tube, a total width of the water bladder and the two springs is relatively large. Therefore, as the width of the water bladder and the two springs is increased, a width of a ceramic cover surrounding the outer periphery thereof is also increased. As a result, the rear portion of the bowl cannot be designed slim, and thus, it is difficult to satisfy a variety of design requests of consumers.
5. The weakest portions of the conventional water closet in view of durability are the bellows tubes where joint motions are continuously performed. A durable material is used to reinforce the weak portions. However, since the lower bellows tube comes into contact with the bottom surface during the lowering motion, it still has a shorter lifespan than the upper bellows tube. That is, the conventional water closet has a durability problem.